Chagas' Disease is a vector-borne parasitic infection of humans with Trypanosoma cruzi, which has recently been identified as an emerging and significant threat to transfusion safety and the blood supply. It is a chronic and potentially fatal condition which affects over 10 million people living in tropical regions of the Americas, is endemic in 21 countries in Latin America in which over 100 million people are at risk of infection, and is responsible for an annual loss of roughly $6.5 billion in economic productivity. The parasite has been found to persist in blood products collected from infected individuals, thereby posing a serious transfusion safety risk. Moreover, Chagas' disease has been imported to non-endemic countries including the United States due to the extensive immigration of residents from Latin America. It has been recently estimated that up to several hundred thousand individuals in the U.S. are currently infected with T. cruzi, many asymptomatically. Recent studies by the American Red Cross and the Centers for Disease Control and Prevention (CDC) have revealed a progressive increase in Chagas' seroprevalence in the U.S., reaching levels as high as one in 5,400 blood donors in areas with large immigrant populations such as Los Angeles. As an inevitable consequence of the rise in Chagas'-positive blood donors, cases of transfusion-transmitted Chagas' disease have been documented in the United States and Canada in recent years. Chagas' disease has also been shown to be transmissible congenitally and by organ transplantation. These facts underscore the increasing attention to Chagas' disease as a public health and blood safety issue, and the need for more effective means to screen and identify T. cruzi - infected individuals and blood donations in the U.S. and worldwide. At present, screening assays have been approved for blood donors, but no validated confirmatory assay exists for Chagas' disease. Radioimmunoprecipitation (RIPA) has been in use for this purpose, but has not been validated and is not readily accessible or practical for the majority of blood bank and clinical laboratory users. In Phase I, we have developed a prototype Chagas immunoblot assay based on a combination of native and recombinant antigens for detection of T. cruzi antibodies and differentiation from cross-reactive pathogens including Leishmania. This assay has shown extremely high sensitivity and specificity in preliminary studies. We propose in Phase II to complete and scale up the immunoblot assay for manufacturing, validate its performance in a clinical study with blood donor and patient serum samples, and submit for regulatory approval for blood screening and clinical diagnostic use.